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Farewell, Rosetta comet mission

ESA’s great Rosetta comet mission has come to an end. Details from its final hour, here.

A last image from the Rosetta spacecraft shortly before impact. Image via @ESA_Rosetta.

UPDATE SEPTEMBER 30. The European Space Agency (ESA) has confirmed it lost contact with spacecraft Rosetta on Friday, September 30, 2016, as the craft crashed into the surface of Comet 67P/Churyumov-Gerasimenko. Confirmation of the end of the mission arrived at ESA’s control centre in Darmstadt, Germany at 11:19 UTC (translate to your time zone) with the loss of Rosetta’s signal upon impact. The controlled descent to the comet’s surface ended Rosetta’s 12-year mission. The spacecraft had been orbiting the comet, following it as it came closest to the sun, since 2014. The world watched live, as the craft descended towards its final resting place on the comet’s surface.

The image above shows the target impact point, which was adjacent to an active pit that the ESA mission team has informally named Deir el-Medina. In describing this image, ESA said:

The target area is home to several active pits measuring over 100 meters across and 60 meters deep [about 100 yards wide and 60 yards deep], from which a number of the comet’s dust jets originate. Some of the pit walls also exhibit intriguing meter-sized lumpy structures called ‘goosebumps’, which could be the signatures of early cometesimals [i.e, the building blocks of comets] that agglomerated to create the comet in the early phases of solar system formation.

Since launch in 2004, Rosetta made six orbits around the sun. Its journey included three Earth flybys, a Mars flyby, and two asteroid encounters.

The craft endured 31 months in deep-space hibernation on the most distant leg of its journey, before waking up in January 2014 and finally arriving at the comet in August 2014.

After becoming the first spacecraft to orbit a comet, and the first to deploy a lander, Philae, in November 2014, Rosetta continued to monitor the comet’s evolution during their closest approach to the sun and beyond. The mission’s operations manager Sylvain Lodiot said:

We’ve operated in the harsh environment of the comet for 786 days, made a number of dramatic flybys close to its surface, survived several unexpected outbursts from the comet, and recovered from two spacecraft ‘safe modes.’

The operations in this final phase have challenged us more than ever before, but it’s a fitting end to Rosetta’s incredible adventure to follow its lander down to the comet.

The video below shows the spacecraft’s final trajectory, as it descended to the surface of its comet.

The next video was made before the final descent and gives more details on what scientists expected to happen.

View larger. | Compilation of the brightest outbursts seen at Comet 67P/Churyumov–Gerasimenko by Rosetta spacecraft between July and September 2015, via ESA.

Since August 9, ESA said, Rosetta had been flying elliptical orbits that brought it progressively closer to the comet. Sylvain Lodiot, ESA’s spacecraft operations manager, said in a September 9 statement:

Although we’ve been flying Rosetta around the comet for two years now, keeping it operating safely for the final weeks of the mission in the unpredictable environment of this comet and so far from the sun and Earth, will be our biggest challenge yet.

We are already feeling the difference in gravitational pull of the comet as we fly closer and closer: it is increasing the spacecraft’s orbital period, which has to be corrected by small manoeuvers.

But this is why we have these flyovers, stepping down in small increments to be robust against these issues when we make the final approach.

View larger. | See the red arced line, top of image? It’s a depiction of the Rosetta spacecraft in early 2016, leaving the inner solar system. Image via Where is Rosetta?

It’s sad to see this wonderful mission end, but exciting to see it go out with such a flourish. Who can forget the thrill two years ago, when Rosetta arrived at its comet? But ending the mission now is logical for several reasons.

For one thing, the comet and spacecraft are getting ever-farther from the sun. The craft is heading out towards the orbit of Jupiter and consequently it’s receiving less sunlight. The solar power needed to operate the craft and its instruments is waning, and there’s been a reduction in the bandwidth available to downlink scientific data back to the European Space Agency (ESA), which spearheaded the mission.

Plus … Rosetta and her instruments are aging. The mission launched on March 2, 2004, aboard an Ariane 5 rocket. On its way toward a rendezvous with its comet, Rosetta made four slingshot flybys to boost its speed via gravitational assist — one around Mars and three around Earth. Now Rosetta has been in the harsh environment of space for over 12 years, the last two of which were in the dusty environment of Comet 67P/Churyumov-Gerasimenko in the most volatile part of its orbit, as it swung in near the sun before and after its perihelion on August 13, 2015.

In addition, beginning around October 1, 2016, if the mission were to continue Rosetta’s operators would be facing reduced communications due to a conjunction of the comet and spacecraft. That is, the comet is now edging into the sun’s glare and will soon be behind the sun as seen from Earth. ESA said this is another contributing factor to concluding the mission in late September.

By September 30, 2016, Rosetta was about 356 million miles (573 million km) from the sun and 447 million miles (720 million km) from Earth.

Before the Rosetta spacecraft mission, who knew comets looked like this? Four-image Rosetta NAVCAM mosaic, using images taken on September 19, 2014 when the spacecraft was 17.8 miles (28.6 km) from Comet 67P/Churyumov-Gerasimenko, via ESA.

View larger. | Rosetta’s location on September 30, 2016, the day of its controlled descent to surface of the comet it’s shadowed since August, 2014. The descent marks the end of the Rosetta mission. Image via ESA.

Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.